1. Field of the Invention
The present invention relates to a differential mechanism built-in type vibration driven motor, which incorporates a differential mechanism for selectively or simultaneously receiving a driving force of an electric motor and an external driving force (e.g., a driving force with a hand), and outputting a synthesized force, and in particular, uses a pencil shaped vibration driven motor.
2. Related Background Art
In recent years, a vibration driven motor has been used as an auto-focus driving source in an exchangeable lens of a camera, and a lens barrel, which can perform a motor-driven auto-focusing operation and a manual focusing operation without requiring a special switching operation, for example, as proposed in Japanese Patent Application Laid-Open No. 2-253212 by the present assignee. The vibration driven motor is formed into a hollow ring shape, and a differential mechanism using, e.g., a ball lace is proposed as a mechanism for switching between the auto-focusing operation and the manual focusing operation. The differential mechanism is also formed into a hollow ring shape to surround the optical lenses in the same manner as the vibration driven motor, and is assembled to the lens barrel integrally with the vibration driven motor.
However, such a differential mechanism built-in type vibration driven motor is suitable for the unique product shape of the lens barrel that surrounds the optical lenses since it has a hollow ring shape. However, in various product specifications and applications, and in particular, in those of the lens barrel, the maximum outer diameter, lens arrangement, and the like tend to be restricted by a motor section, resulting in poor versatility. Needless to say, a vibration driven motor need not have a hollow ring shape in terms of space and layout upon application to products other than a lens barrel, e.g., audio equipment.
The hollow ring-shaped vibration driven motor suffers from high cost, and requires cumbersome, time-consuming steps of bonding a piezo-electric element for generating a vibration to a ring-shaped vibration elastic body by an adhesive, and of performing a polarization treatment.
Thus, it is desired to integrally assemble a differential mechanism to a pencil shape vibration driven motor, which utilizes an ultrasonic vibration similar to the hollow ring-shaped vibration driven motor, but can be easily manufactured and rendered as small as a little finger of a person, whereby, for example, motor and manual driving operations can be desirably switched, a synthesized force of these operations can be output, and a compact structure can be realized.